Recently, due to the continuous development of semiconductor processing technology, the biomedical micro-sensing technology also has significant growth on its development. In the domain of bio-sensing technology, it could be approximately divided into two types of inspection methods, i.e. inspection on chemical reaction amount and physical reaction amount. However, it could be classified into electrochemical theory and electromagnetic theory based on the inspection theory, in which the electromagnetic theory includes the optical inspection, electrical inspection, sound wave inspection and microwave inspection methods.
The Surface Plasmon Resonance (SPR) method and the Raman Spectrum measurement method are the current dominant sensing technologies. However, for the inspection system of these inspection methods, the important components, such as laser source, optical loop system, and optical components, are difficult to be miniaturized, so that the entire inspection system could not be developed toward a complete micro system. Moreover, for the technology of sound wave inspection and microwave inspection, it employs the Surface Acoustic Wave (SAW) transducer and quartz crystal microbalance (QCM) transducer as the major inspection components, in which both of the SAW transducer and the QCM transducer employ the piezoelectric quartz crystal as the material. The SAW transducer is excited by applying voltage on the metal film inter digital transducer (IDT) on the surface having piezoelectric material, so, when the boundary conditions on the wave conduction path have been changed, the characteristics of sound wave, such as wave speed, phase or amplitude, will also be changed accordingly. The QCM transducer uses the quartz crystal itself as the material, which employs the frequency generated by the oscillation of quartz crystal itself to detect the variation on the concentration of the inspected subject, and the outcome comes from the characteristic of inversed piezoelectric effect of the quartz itself. When applying electric field on the surface of the quartz crystal, the quartz crystal will be oscillated to achieve the purpose of detecting the concentration variation.
The SAW and QCM transducer themselves both have multiple advantages, such as simplified theory, easy operation, low cost, repetitive use of chips, light instrument, and real-time response. However, due to a certain limitation on the working frequency, the typical working frequency of the SAW transducer is only at hundreds of MHz, and the typical working frequency of the QCM transducer is only at tens of MHz. Because of the influence by the limitation from the intrinsic physical characteristics, both inspection methods are subjected to great limitations on the sensitivity, resolution and Signal-to-Noise ratio (SNR).